I've looked at these posts:
http://empegbbs.com/ubbthreads/showflat....=true#Post12725
http://empegbbs.com/ubbthreads/showflat....true#Post255739
http://empegbbs.com/ubbthreads/showflat....true#Post228316

And I was wondering if it would work if I got a y-connector and plugged 2 RCA cables into the front input L&R ports? Like the other people who asked about this, I have a GPS device that has a normal headphone wire for output. I have the cables to plug this into an RCA port, and I'm not sure what would happen if there were two audio sources going into the amp at the same time Hopefully, it would play both at the same time.

Has anybody tried this or know that it won't work? Or do you know that it will work?

No, you cannot combine two audio outputs into one input with just a Y cable.

You can split one output to two separate amplifiers that way, but not the other way around.

You must use a mixer circuit, even a simple resistance mixer circuit would do. That's just a certain value of resistor in the right place.

The third threads you linked has a link to the simplest resistance mixer. Go here and scroll down to the part where it says "can I make this circuit even simpler".

That seems easy enough, thanks!

Now to find the time to modify two y-connectors with 10k resistors on the negative side. The simple circuit looks like two mono connections being combined instead of two stereo ones? I should need 4 resistors, right? (R5, R6, R7, R8 in the top diagram)

Even though it took me 3.5 months to get around to doing this project, I got it done, and it works. My car now talks to me with my GPS running MS Streets & Trips 2006.

Thanks!